This research paper presents the results of an educational experiment to measure the effects of different instructional behaviors. The experiment investigated a controlling style of teaching compared to an autonomy supportive style, and found that the supportive style resulted in increased student interest, enjoyment, engagement and performance. Autonomy-supportive teacher behavior can be effective in fostering intrinsic motivation in students. The paper provides useful background information on the topics of motivation, intentionality and autonomy, and also gives examples of controlling vs. supportive teacher behaviors.